1. Preheat the oven to 180c/350f/gas mark 4.
2. Finely chop the onion, celery, garlic, peel the sweet potato and cut into rounds about 1/4 inch thick.
3. Sprinkle flour on a plate, season with salt and pepper then toss the chicken thighs so thoroughly coated.
4. In a casserole dish, add the ol...